<body>
Nilai a : <input type="text" name="a" id="a"><br/><br/>
<select name="oper" id="o">
<option value="tambah" class="tambah"> + </option>
<option value="kurang" class="kurang"> - </option>
<option value="kali" class="kali"> x </option>
<option value="bagi" class="bagi"> / </option>
</select><br>
Nilai c : <input type="text" name="b" id="c"><br/><br/>
<button class="btn2">Hitung</button>
<p id="hasil"></p>
</body>
<script>
$(document).on("click",".btn2",function(e){
var a = parseInt($("#a").val());
var c = parseInt($("#c").val());
var rumus_jumlah = a+c;
var rumus_kurang = a-c;
var rumus_kali
= a*c;
var rumus_bagi = a/c;
$("#o").change(function () {
if ($("#o").val() == "tambah"){
$("#hasil").html("Hasil dari Penjumlahan = "+ rumus_jumlah);
}
});
});
</script>